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XLI. Intelligence and Miscellaneous Articles. 



ON THE DIFFERENCE IN SIZE OF MEDALS OF DIFFERENT METALS 

 OBTAINED BY STAMPING, AND BY CASTING IN THE SAME 

 MOULD. BY H. W. DOVE. 



T> AUDRIMONT has found {Ann. de Chim. et de Phys.voh Ix. p. 78) 

 -"-* that wires of different metals drawn through the same press are 

 not all of the same thickness ; for they are of different degrees of 

 elasticity, and after being drawn through the press they expand to 

 different amounts, This expansion is proved by the fact that, with 

 the exception of gold wire, no wire can be drawn through the same 

 aperture through which it has been pressed. Silver requires the 

 least force, but the expansion caused by elasticity continues for 

 several weeks. 



It appeared probable that in stamping medals something similar 

 would prevail, and that medals of different metals stamped in the 

 same die would be different in size. This is most readily seen in those 

 medals in which the impression is symmetrically arranged in reference 

 to the edge, as is the case with the medals of the French Exhibition, 

 in which the coats of arms encircle the French eagle in the middle. 

 One of those in silver, and one in bronze were placed in the stereo- 

 scope, the eagle being fixed in the middle. After some time the 

 stereoscopic combined medal was seen in the form of a hollow escut- 

 cheon, and of the colour of an alloy of the two metals. Evidently 

 the reason of this lies in the nonius-like shifting of the individual lines 

 of the impression. This result, which I have described (Optische Stu- 

 dien, p. 29), I have also obtained with large gold and silver medals 

 which were kindly entrusted to me from the Royal Mint in Berlin. 

 It was probable that medals obtained by casting would show the 

 same thing, and this was found to be the case with tin, bismuth, 

 and lead. The casts were very beautifully executed for me for this 

 purpose by Professor Kiss. Hiero's crown led to the application of 

 specific gravity to detect an adulteration ; the stereoscope is a new 

 means. — Poggendorff's Annalen, vol. ex. p. 498. 



ON ATMOSPHERIC ELECTRICITY. BY M. VOLPICELLI. 



Of the two characters which distinguish electricity, its tension 

 and its nature, the first depends on the hygrometric state of the 

 atmosphere, and the second is independent of it. The author de- 

 scribes a series of experiments on the latter point made on days which 

 were not stormy. 



1st. The upper extremity of a copper rod, well insulated and 

 fixed on the roof of the Physical Museum of the University of Rome, 

 was 45 m, 39 high above the sea-level. If the upper end terminated 



